This invention relates to a control method and control device for controlling an actuator to move a head to a target position in a disk storage device, that reads or reads/writes information from a disk storage medium by the head.
Disk storage devices such as magnetic disk drives or optical disk drives are widely used as storage devices for computers and the like. In these kinds of disk storage devices, eccentricity of the disk medium occurs. This eccentricity occurs when the center of rotation of the disk medium that was recorded the position information shifts when that of writing the position information.
In the sector servo method, the position information (servo information) for detecting the actuator position is recorded on each disk surface. This position information is formed on concentric circles. When the center of rotation of the disk matches with the center of rotation of the disk when the position information was written, then ideally no eccentricity will occur.
However, in actuality, the centers of rotation do not match and eccentricity occurs. The reason for this is probably due to thermal deformation of the disk medium and a spindle shaft, or shifting of the disk due to external impact. When there is eccentricity, it can be seen from the actuator""s point of view that sinusoidal disturbance on the order of integral multiples of the rotation frequency is applied. Therefore, a technique for correcting this eccentricity is necessary.
Control using an eccentricity estimation observer (estimator) has been known as a technique for correcting this eccentricity. In the control by this eccentricity estimation observer, steady position control by the estimated values is required.
FIG. 12 is a configuration drawing of this prior art, and FIG. 13 is a drawing for explaining this prior art.
Position control of a magnetic head by the use of an eccentricity estimation observer is described in detail in Japanese Unexamined Published patent No. 7-50075 (U.S. Pat. No. 5,404,235). Therefore, the eccentricity estimation observer will only be simply explained here.
First, an ideal actuator model that does not include resonance will be considered. Here, when xe2x80x98x1xe2x80x99 is taken to be the position, xe2x80x98x2xe2x80x99 the velocity, xe2x80x98yxe2x80x99 the observed position (detected position), xe2x80x98uxe2x80x99 the control current and xe2x80x98sxe2x80x99 the Laplace operator, then the state equations are given by equations (1) and (2) below.                               S          ⁡                      (                                                                                X                    1                                                                                                                    X                    2                                                                        )                          =                                            (                                                                    0                                                        1                                                                                        0                                                        0                                                              )                        ⁢                          (                                                                                          X                      1                                                                                                                                  X                      2                                                                                  )                                +                                    Kp              ⁡                              (                                                                            0                                                                                                  1                                                                      )                                      ⁢            u                                              (        1        )                                y        =                              (                                                            1                                                  0                                                      )                    ⁢                      (                                                                                X                    1                                                                                                                    X                    2                                                                        )                                              (        2        )            
Here, xe2x80x98Kpxe2x80x99 is the acceleration constant when rotating type actuator of the model is considered to be an equivalent linear type actuator.
When considering the current feedback, the steady-state current (bias current) state xe2x80x98x3xe2x80x99 is added to the state equations, and thus the state equations are given by equations (3) and (4) below.                               S          ⁡                      (                                                                                X                    1                                                                                                                    X                    2                                                                                                                    X                    3                                                                        )                          =                                            (                                                                    0                                                        1                                                        0                                                                                        0                                                        0                                                                              K                      p                                                                                                            0                                                        0                                                        0                                                              )                        ⁢                          (                                                                                          X                      1                                                                                                                                  X                      2                                                                                                                                  X                      3                                                                                  )                                +                                    Kp              ⁡                              (                                                                            0                                                                                                  1                                                                                                  0                                                                      )                                      ⁢            u                                              (        3        )                                y        =                              (                          1              ⁢                              xe2x80x83                            ⁢              0              ⁢                              xe2x80x83                            ⁢              0                        )                    ⁢                      (                                                                                X                    1                                                                                                                    X                    2                                                                                                                    X                    3                                                                        )                                              (        4        )            
Furthermore, the eccentricity disturbance state is added to these state equations. When xe2x80x98x4xe2x80x99 and xe2x80x98x5xe2x80x99 are taken to be the state variable of the eccentricity, and xe2x80x98xcfx890xe2x80x99 is taken to be the eccentric angular velocity, then the state equations are given by equations (5) and (6) below.                               S          ⁡                      (                                                                                X                    1                                                                                                                    X                    2                                                                                                                    X                    3                                                                                                                    X                    4                                                                                                                    X                    5                                                                        )                          =                                            (                                                                    0                                                        1                                                        0                                                        0                                                        0                                                                                        0                                                        0                                                        Kp                                                        Kp                                                        0                                                                                        0                                                        0                                                        0                                                        0                                                        0                                                                                        0                                                        0                                                        0                                                        0                                                        1                                                                                        0                                                        0                                                        0                                                                              -                                              ω                        0                        2                                                                                                  0                                                              )                        ⁢                          (                                                                                          X                      1                                                                                                                                  X                      2                                                                                                                                  X                      3                                                                                                                                  X                      4                                                                                                                                  X                      5                                                                                  )                                +                                    Kp              ⁡                              (                                                                            0                                                                                                  1                                                                                                  0                                                                                                  0                                                                                                  0                                                                      )                                      ⁢            u                                              (        5        )                                y        =                              (                          1              ⁢                              xe2x80x83                            ⁢              0              ⁢                              xe2x80x83                            ⁢              0              ⁢                              xe2x80x83                            ⁢              0              ⁢                              xe2x80x83                            ⁢              0                        )                    ⁢                      (                                                                                X                    1                                                                                                                    X                    2                                                                                                                    X                    3                                                                                                                    X                    4                                                                                                                    X                    5                                                                        )                                              (        6        )            
Here, when x4=cos(xcfx890xc2x7t) and x5=sin(xcfx890xc2x7t), then sx4 =xe2x88x92xcfx890xc2x7sin(w0xc2x7t) and sx5=xcfx890 xc2x7cos(xcfx890xc2x7t), so sx4=xe2x88x92xcfx890xc2x7x5and sx5=xcfx890xc2x7x4. Therefore, the state equations (5) and (6) are given by equations (7) and (8) below.                               S          ⁡                      (                                                                                X                    1                                                                                                                    X                    2                                                                                                                    X                    3                                                                                                                    X                    4                                                                                                                    X                    5                                                                        )                          =                                            (                                                                    0                                                        1                                                        0                                                        0                                                        0                                                                                        0                                                        0                                                        Kp                                                        Kp                                                        0                                                                                        0                                                        0                                                        0                                                        0                                                        0                                                                                        0                                                        0                                                        0                                                        0                                                                              -                                              ω                        0                                                                                                                                  0                                                        0                                                        0                                                                              ω                      0                                                                            0                                                              )                        ⁢                          (                                                                                          X                      1                                                                                                                                  X                      2                                                                                                                                  X                      3                                                                                                                                  X                      4                                                                                                                                  X                      5                                                                                  )                                +                                    Kp              ⁡                              (                                                                            0                                                                                                  1                                                                                                  0                                                                                                  0                                                                                                  0                                                                      )                                      ⁢            u                                              (        7        )                                y        =                              (                          1              ⁢                              xe2x80x83                            ⁢              0              ⁢                              xe2x80x83                            ⁢              0              ⁢                              xe2x80x83                            ⁢              0              ⁢                              xe2x80x83                            ⁢              0                        )                    ⁢                      (                                                                                X                    1                                                                                                                    X                    2                                                                                                                    X                    3                                                                                                                    X                    4                                                                                                                    X                    5                                                                        )                                              (        8        )            
In equation (5) the eccentricity is estimated by the sinusoidal transfer function (1/(S2+xcfx8902)). As shown in FIG. 13, equation (7) shows the movement in rectangular coordinates (x4,x5) of a point on the circle with radius (x4{circumflex over ( )}2+x5{circumflex over ( )}2) that is rotating at constant velocity.
The observer is designed to transfer the state equations (7) and (8) to a discrete form. The equations are transferred into a discrete form by estimating the zero-dimension hold. In other words, it performs Z conversion. By considering the time lag from when the position is detected until current is output to the actuator, state equations become 6 dimensional. Even when not considered, the state equations are given by equations (9) and (10) below.                               (                                                                                          X                    1                                    ⁡                                      [                                          K                      ⁢                                              xe2x80x83                                            +                                              xe2x80x83                                            ⁢                      1                                        ]                                                                                                                                            X                    2                                    ⁡                                      [                                          K                      ⁢                                              xe2x80x83                                            +                                              xe2x80x83                                            ⁢                      1                                        ]                                                                                                                                            X                    3                                    ⁡                                      [                                          K                      ⁢                                              xe2x80x83                                            +                                              xe2x80x83                                            ⁢                      1                                        ]                                                                                                                                            X                    4                                    ⁡                                      [                                          K                      ⁢                                              xe2x80x83                                            +                                              xe2x80x83                                            ⁢                      1                                        ]                                                                                                                                            X                    5                                    ⁡                                      [                                          K                      ⁢                                              xe2x80x83                                            +                                              xe2x80x83                                            ⁢                      1                                        ]                                                                                )                =                                            (                                                                    1                                                        T                                                                                                      KpT                        2                                            2                                                                                                                          Kp                                                  ω                          0                          2                                                                    ⁢                                              xe2x80x83                                            ⁢                                              (                                                  1                          ⁢                                                      xe2x80x83                                                    -                                                      xe2x80x83                                                    ⁢                                                      cos                            ⁡                                                          (                                                                                                ω                                  0                                                                ⁢                                                                  xe2x80x83                                                                ⁢                                T                                                            )                                                                                                      )                                                                                                                                                Kp                                                  ω                          0                          2                                                                    ⁢                                              xe2x80x83                                            ⁢                                              (                                                                                                            ω                              0                                                        ⁢                                                          xe2x80x83                                                        ⁢                            T                                                    ⁢                                                      xe2x80x83                                                    -                                                      xe2x80x83                                                    ⁢                                                      sin                            ⁡                                                          (                                                                                                ω                                  0                                                                ⁢                                                                  xe2x80x83                                                                ⁢                                T                                                            )                                                                                                      )                                                                                                                                  0                                                        1                                                        KpT                                                                                                                                                            Kp                            ⁢                                                          xe2x80x83                                                        -                                                          xe2x80x83                                                        ⁢                                                          sin                              ⁡                                                              (                                                                                                      ω                                    0                                                                    ⁢                                                                      xe2x80x83                                                                    ⁢                                  T                                                                )                                                                                                              )                                                ⁢                                                  xe2x80x83                                                                                            ω                        0                                                                                                                                                Kp                                                  ω                          0                                                                    ⁢                                              xe2x80x83                                            ⁢                                              (                                                  1                          ⁢                                                      xe2x80x83                                                    -                                                      xe2x80x83                                                    ⁢                                                      cos                            ⁡                                                          (                                                                                                ω                                  0                                                                ⁢                                                                  xe2x80x83                                                                ⁢                                T                                                            )                                                                                                      )                                                                                                                                  0                                                        0                                                        1                                                        0                                                        0                                                                                        0                                                        0                                                        0                                                                              cos                      ⁡                                              (                                                                              ω                            0                                                    ⁢                                                      xe2x80x83                                                    ⁢                          T                                                )                                                                                                                        -                                              sin                        ⁡                                                  (                                                                                    ω                              0                                                        ⁢                                                          xe2x80x83                                                        ⁢                            T                                                    )                                                                                                                                                          0                                                        0                                                        0                                                                              sin                      ⁡                                              (                                                                              ω                            0                                                    ⁢                                                      xe2x80x83                                                    ⁢                          T                                                )                                                                                                                        cos                      ⁡                                              (                                                                              ω                            0                                                    ⁢                                                      xe2x80x83                                                    ⁢                          T                                                )                                                                                                        )                        ⁢                          (                                                                                                                  X                        1                                            ⁡                                              [                        K                        ]                                                                                                                                                                                X                        2                                            ⁡                                              [                        K                        ]                                                                                                                                                                                X                        3                                            ⁡                                              [                        K                        ]                                                                                                                                                                                X                        4                                            ⁡                                              [                        K                        ]                                                                                                                                                                                X                        5                                            ⁡                                              [                        K                        ]                                                                                                        )                                +                                    Kp              ⁡                              (                                                                                                                              T                          2                                                /                        2                                                                                                                        T                                                                                                  0                                                                                                  0                                                                                                  0                                                                      )                                      ⁢                          u              ⁡                              [                k                ]                                                                        (        9        )                                          y          ⁡                      [            k            ]                          =                              (                          1              ⁢                              xe2x80x83                            ⁢              0              ⁢                              xe2x80x83                            ⁢              0              ⁢                              xe2x80x83                            ⁢              0              ⁢                              xe2x80x83                            ⁢              0                        )                    ⁢                      (                                                                                                      X                      1                                        ⁡                                          [                      K                      ]                                                                                                                                                              X                      2                                        ⁡                                          [                      K                      ]                                                                                                                                                              X                      3                                        ⁡                                          [                      K                      ]                                                                                                                                                              X                      4                                        ⁡                                          [                      K                      ]                                                                                                                                                              X                      5                                        ⁡                                          [                      K                      ]                                                                                            )                                              (        10        )            
Here, T is the sample period. As shown in equation (11), the coefficients in equations (9) and (10) are A, B and C.                                                                         A                =                                  (                                                                                    1                                                                    T                                                                                                                          KpT                            2                                                    2                                                                                                                                                  Kp                                                          ω                              0                              2                                                                                ⁢                                                      xe2x80x83                                                    ⁢                                                      (                                                          1                              ⁢                                                              xe2x80x83                                                            -                                                              xe2x80x83                                                            ⁢                                                              cos                                ⁡                                                                  (                                                                                                            ω                                      0                                                                        ⁢                                                                          xe2x80x83                                                                        ⁢                                    T                                                                    )                                                                                                                      )                                                                                                                                                                            Kp                                                          ω                              0                              2                                                                                ⁢                                                      xe2x80x83                                                    ⁢                                                                                    (                                                                                                                                    ω                                    0                                                                    ⁢                                                                      xe2x80x83                                                                    ⁢                                  T                                                                ⁢                                                                  xe2x80x83                                                                -                                                                  xe2x80x83                                                                ⁢                                                                  sin                                  ⁡                                                                      (                                                                                                                  ω                                        0                                                                            ⁢                                                                              xe2x80x83                                                                            ⁢                                      T                                                                        )                                                                                                                              )                                                        ⁢                                                          xe2x80x83                                                                                                                                                                                          0                                                                    1                                                                    KpT                                                                                                                                                                                        Kp                                ⁢                                                                  xe2x80x83                                                                -                                                                  xe2x80x83                                                                ⁢                                                                  sin                                  ⁡                                                                      (                                                                                                                  ω                                        0                                                                            ⁢                                                                              xe2x80x83                                                                            ⁢                                      T                                                                        )                                                                                                                              )                                                        ⁢                                                          xe2x80x83                                                                                                            ω                            0                                                                                                                                                                            Kp                                                          ω                              0                                                                                ⁢                                                      xe2x80x83                                                    ⁢                                                      (                                                          1                              ⁢                                                              xe2x80x83                                                            -                                                              xe2x80x83                                                            ⁢                                                              cos                                ⁡                                                                  (                                                                                                            ω                                      0                                                                        ⁢                                                                          xe2x80x83                                                                        ⁢                                    T                                                                    )                                                                                                                      )                                                                                                                                                              0                                                                    0                                                                    1                                                                    0                                                                    0                                                                                                            0                                                                    0                                                                    0                                                                                              cos                          ⁡                                                      (                                                                                          ω                                0                                                            ⁢                                                              xe2x80x83                                                            ⁢                              T                                                        )                                                                                                                                                -                                                      sin                            ⁡                                                          (                                                                                                ω                                  0                                                                ⁢                                                                  xe2x80x83                                                                ⁢                                T                                                            )                                                                                                                                                                                          0                                                                    0                                                                    0                                                                                              sin                          ⁡                                                      (                                                                                          ω                                0                                                            ⁢                                                              xe2x80x83                                                            ⁢                              T                                                        )                                                                                                                                                cos                          ⁡                                                      (                                                                                          ω                                0                                                            ⁢                                                              xe2x80x83                                                            ⁢                              T                                                        )                                                                                                                                )                                            ,                                                                          B              =                              Kp                ⁡                                  (                                                                                                                                          T                            2                                                    /                          2                                                                                                                                    T                                                                                                            0                                                                                                            0                                                                                                            0                                                                              )                                                                                                        C              ⁢                              xe2x80x83                            =                              xe2x80x83                            ⁢                              (                                  1                  ⁢                                      xe2x80x83                                    ⁢                  0                  ⁢                                      xe2x80x83                                    ⁢                  0                  ⁢                                      xe2x80x83                                    ⁢                  0                  ⁢                                      xe2x80x83                                    ⁢                  0                                )                                                                        (        11        )            
Here, the observer is expressed by the equations (12), (13) and (14) below.                               (                                                                                          PX                    1                                    ⁡                                      [                                          K                      ⁢                                              xe2x80x83                                            +                                              xe2x80x83                                            ⁢                      1                                        ]                                                                                                                                            PX                    2                                    ⁡                                      [                                          K                      ⁢                                              xe2x80x83                                            +                                              xe2x80x83                                            ⁢                      1                                        ]                                                                                                                                            PX                    3                                    ⁡                                      [                                          K                      ⁢                                              xe2x80x83                                            +                                              xe2x80x83                                            ⁢                      1                                        ]                                                                                                                                            PX                    4                                    ⁡                                      [                                          K                      ⁢                                              xe2x80x83                                            +                                              xe2x80x83                                            ⁢                      1                                        ]                                                                                                                                            PX                    5                                    ⁡                                      [                                          K                      ⁢                                              xe2x80x83                                            +                                              xe2x80x83                                            ⁢                      1                                        ]                                                                                )                =                              A            ⁡                          (                                                                                                                  PX                        1                                            ⁡                                              [                        K                        ]                                                                                                                                                                                PX                        2                                            ⁡                                              [                        K                        ]                                                                                                                                                                                PX                        3                                            ⁡                                              [                        K                        ]                                                                                                                                                                                PX                        4                                            ⁡                                              [                        K                        ]                                                                                                                                                                                PX                        5                                            ⁡                                              [                        K                        ]                                                                                                        )                                +                      B            ·                          u              ⁡                              [                k                ]                                              +                                    (                                                                                          L                      1                                                                                                                                  L                      2                                                                                                                                  L                      3                                                                                                                                  L                      4                                                                                                                                  L                      5                                                                                  )                        ⁢                          (                                                y                  ⁡                                      [                    k                    ]                                                  ⁢                                  xe2x80x83                                -                                  xe2x80x83                                ⁢                                                      PX                    1                                    ⁡                                      [                    k                    ]                                                              )                                                          (        12        )                                          py          ⁡                      [            k            ]                          =                  C          ⁡                      (                                                                                                      PX                      1                                        ⁡                                          [                      K                      ]                                                                                                                                                              PX                      2                                        ⁡                                          [                      K                      ]                                                                                                                                                              PX                      3                                        ⁡                                          [                      K                      ]                                                                                                                                                              PX                      4                                        ⁡                                          [                      K                      ]                                                                                                                                                              PX                      5                                        ⁡                                          [                      K                      ]                                                                                            )                                              (        13        )                                          u          ⁡                      [            k            ]                          =                              -                          (                                                F                  1                                ⁢                                  xe2x80x83                                ⁢                                  F                  2                                ⁢                                  xe2x80x83                                ⁢                1                ⁢                                  xe2x80x83                                ⁢                1                ⁢                                  xe2x80x83                                ⁢                0                            )                                ⁢                      (                                                                                                      PX                      1                                        ⁡                                          [                      K                      ]                                                                                                                                                              PX                      2                                        ⁡                                          [                      K                      ]                                                                                                                                                              PX                      3                                        ⁡                                          [                      K                      ]                                                                                                                                                              PX                      4                                        ⁡                                          [                      K                      ]                                                                                                                                                              PX                      5                                        ⁡                                          [                      K                      ]                                                                                            )                                              (        14        )            
Here, px1 is the state variable for position (estimated position), px2 is the state variable for velocity (estimated velocity), px3 is the state variable for the bias current (estimated bias current), px4 and px5 are state variable for the eccentricity (estimated eccentricity), xe2x80x98uxe2x80x99 is the control current, xe2x80x98yxe2x80x99 is the observed position (detected position) and xe2x80x98pyxe2x80x99 is the estimated position.
Moreover, L1 to L5 are the estimation gains of the observer, where L1 is the position estimation gain, L2 is the velocity estimation gain, L3 is the bias estimation gain, and L4 and L5 are the eccentricity estimation gains. Furthermore, F1 to F5 are the state feedback matrix.
When this is shown in a block diagram, a diagram as shown in FIG. 12 is obtained. In other words, a plant 90 shows the portion that performs real positioning of the head of a magnetic disk drive, and includes an actuator, AMP and magnetic heads. The observer (estimator) 91 estimates the position, velocity, bias and eccentricity from the current state, and outputs control current.
The position signal (servo signal) y[k] that is read by the magnetic head is output from the plant 90. The observer 91 calculates the error (y[k]xe2x88x92px1[k]) between the position signal y[k] and the estimated position py[k] (=px1[k]). The error is input to the fourth gain multiplier 96. The gain multiplier 96 multiplies the error by the estimation gain L (L2 to L5) (see equation (12)). L1 to L3 is the estimated operating gain of the actuator, and L4 and L5 are the eccentricity estimation gain.
The second gain multiplier 94 multiplies the control current u[k] by the coefficient B (see equation (12)). The third gain multiplier 95 multiplies the state signal px[k] at the time of this sample by coefficient A (see equation (12)). An adder 98 adds the outputs from the three adders 94 to 96. From this the state signal px[k+1] for the next sample of equation (12) is output.
This state signal px[k+1] for the next sample is delayed one sample by an delay circuit 99 to obtain the state signal px[k] for this sample. This state signal px[k] is then multiplied by a feedback coefficient xe2x80x98Cxe2x80x99 by a fifth multiplier 97. From this, the estimated position py[k] for this sample, as given by Equation (13), is obtained.
Furthermore, the state signal px[k] is multiplied by the feedback coefficient xe2x80x98Fxe2x80x99 by a first multiplier 93. From this, the control current u[k] for this time, as given by Equation (14), is obtained. This control current u[k] is supplied to the plant 90.
In this way, the observer 91 is comprised by an eccentricity estimation observer including the actuator model and eccentric model, and it predicts the next state from the error between the detected position and estimated position, the control current and the state variables, and creates a control current from the state. In this way, the eccentricity is corrected in real time making it possible to quickly correct. In this prior art, a control signal was created by a similar configuration during seek control time as well.
However, this prior art had the following problems.
First, during seeking, the actuator moves at high speed so it may move more than 50 tracks per sample. When it moves at high speed like this, it is not possible to accurately detect the position for each sample. Therefore, the eccentricity estimation observer estimates the amount of eccentricity from the position error and thus error occurs in the estimated amount of eccentricity. It is a long time that the eccentricity state converges if there is the error, because convergence is slow at about 90 Hertz. This becomes a problem in that convergence at the end of seeking becomes slow.
Second, when seeking over a long distance, the output current of the current amp becomes saturated. The maximum current during saturation differs depending on the power-supply voltage or the actuator resistance, and it is greatly affected by variations in differences in the environment and equipment. Therefore, since the eccentricity estimation observer does not predict the saturation of the output current of the current amp, errors occur in the amount of eccentricity that is estimated from the position error. Therefore, there was the problem the convergence becomes slow after seeking.
The objective of this invention is to provide a control method and control device for a disk storage device that prevent a slow convergence when seek end.
Another objective of this invention is to provide a control method and control device for a disk storage device that prevent a slow convergence when seek end even when eccentricity correction is performed.
A further objective of this invention is to provide a control method and control device for a disk storage device that prevent a position error from affecting the estimated value for the eccentricity.
The disk storage device of this invention comprises: a disk storage medium, a head for reading information on the disk storage medium, an actuator for moving the head, and a control circuit, that uses eccentricity estimation observer control that includes an actuator model and eccentric model, for calculating a control signal for driving the actuator based on a position signal that is read from the disk storage medium by the head.
In addition, the control method and device of this invention comprises: a step of selecting a first eccentricity estimation gain during seek control, and for selecting a second eccentricity estimation gain during following control; and a step of calculating a state signal, which includes the estimated position, estimated velocity, estimated bias signal and estimated eccentricity signal, and which is based on the estimated actuator gain, that estimates the actuator operation, and the selected eccentricity estimation gain, and of calculating the control signal from the state signal.
In this invention, the amount of eccentricity is not estimated from the position error during seeking since large errors occur on the amount of eccentricity when estimating it from the position error during seeking. However, in order for a steady seek operation, it is necessary to correct the eccentricity. Therefore, this invention minimizes the eccentricity estimation gains L4, L5 of the eccentricity estimation observer during seek more than during following, to prevent the position error from affecting the estimated amount of eccentricity.
For example, during seeking, the eccentricity estimation gains L4, L5 are taken to be xe2x80x980xe2x80x99. By doing this, the state equation (12) becomes equation (15) below.                               (                                                                                          PX                    1                                    ⁡                                      [                                          K                      ⁢                                              xe2x80x83                                            +                                              xe2x80x83                                            ⁢                      1                                        ]                                                                                                                                            PX                    2                                    ⁡                                      [                                          K                      ⁢                                              xe2x80x83                                            +                                              xe2x80x83                                            ⁢                      1                                        ]                                                                                                                                            PX                    3                                    ⁡                                      [                                          K                      ⁢                                              xe2x80x83                                            +                                              xe2x80x83                                            ⁢                      1                                        ]                                                                                                                                            PX                    4                                    ⁡                                      [                                          K                      ⁢                                              xe2x80x83                                            +                                              xe2x80x83                                            ⁢                      1                                        ]                                                                                                                                            PX                    5                                    ⁡                                      [                                          K                      ⁢                                              xe2x80x83                                            +                                              xe2x80x83                                            ⁢                      1                                        ]                                                                                )                =                              A            ⁡                          (                                                                                                                  PX                        1                                            ⁡                                              [                        K                        ]                                                                                                                                                                                PX                        2                                            ⁡                                              [                        K                        ]                                                                                                                                                                                PX                        3                                            ⁡                                              [                        K                        ]                                                                                                                                                                                PX                        4                                            ⁡                                              [                        K                        ]                                                                                                                                                                                PX                        5                                            ⁡                                              [                        K                        ]                                                                                                        )                                +                      B            ·                          u              ⁡                              [                k                ]                                              +                                    (                                                                                          L                      1                                                                                                                                  L                      2                                                                                                                                  L                      3                                                                                                            0                                                                                        0                                                              )                        ⁢                          (                                                y                  ⁡                                      [                    k                    ]                                                  ⁢                                  xe2x80x83                                -                                  xe2x80x83                                ⁢                                                      PX                    1                                    ⁡                                      [                    k                    ]                                                              )                                                          (        15        )            
In this equation (15), by calculating the state variables X4 and X5 for eccentricity, the equation (16) below is obtained.                               (                                                                                          PX                    4                                    ⁡                                      [                                          K                      ⁢                                              xe2x80x83                                            +                                              xe2x80x83                                            ⁢                      1                                        ]                                                                                                                                            PX                    5                                    ⁡                                      [                                          K                      ⁢                                              xe2x80x83                                            +                                              xe2x80x83                                            ⁢                      1                                        ]                                                                                )                =                              (                                                                                cos                    ⁡                                          (                                                                        ω                          0                                                ⁢                                                  xe2x80x83                                                ⁢                        T                                            )                                                                                                            -                                          sin                      ⁡                                              (                                                                              ω                            0                                                    ⁢                                                      xe2x80x83                                                    ⁢                          T                                                )                                                                                                                                                              sin                    ⁡                                          (                                                                        ω                          0                                                ⁢                                                  xe2x80x83                                                ⁢                        T                                            )                                                                                                            cos                    ⁡                                          (                                                                        ω                          0                                                ⁢                                                  xe2x80x83                                                ⁢                        T                                            )                                                                                            )                    ⁢                      (                                                                                                      PX                      4                                        ⁡                                          [                      K                      ]                                                                                                                                                              PX                      5                                        ⁡                                          [                      K                      ]                                                                                            )                                              (        16        )            
In equation (16), the state variable X4 and X5 for eccentricity become unrelated to the observed position y and estimated position x1. In other words, state variables X4 and X5 that are not affected by the position error (y[k] - x1[k]) are obtained. In equation (16), xcfx890T is the phase for one sample. In addition, equation (16) shows that the current state variables have a phase shift of only one sample. In other words, equation (16) is a sinusoidal recursive equation.
Therefore, it is possible to prevent the position error from affecting the estimated eccentricity value when seeking. Moreover, it is possible to quicken the convergence operation after seeking. Also, as shown in equation (16), since the eccentricity is corrected during seeking, there is no loss of stability during seeking. The eccentricity estimation gain during seek, does not need to be xe2x80x980xe2x80x99, but can be a value near xe2x80x980xe2x80x99.
Moreover, another form of the invention further comprises a step of detecting the position error between the target position and the current position, and a step of determining that control is the aforementioned following control when the position error is within a specified range, and of determining that control is the aforementioned seek control when the position error exceeds the specified value by comparing the position error and the specified values.
Furthermore, in another form of the invention, the calculation step comprises: a first calculation step of calculating the estimated position signal, estimated velocity signal and estimated eccentricity signal for the next sample from the estimated position signal, estimated velocity signal, estimated eccentricity signal, estimated actuator gain and eccentricity estimation gain of the current sample; and a second calculation step of calculating the control current from estimated position signal, estimated velocity signal and estimated eccentricity signal of the current sample. In other words, the eccentricity estimation observer is a prediction observer.
In yet another form of the invention, the aforementioned first calculation step comprises: a third calculation step of calculating the estimated position signal and estimated velocity signal for the next sample from the estimated position signal, estimated velocity signal and estimated actuator gain of the current sample; and a fourth calculation step of calculating the estimated eccentricity signal for the next sample from the estimated eccentricity signal and from the eccentricity estimation gain of the current sample.
In this form of the invention, the calculation of estimating the actuator operation is separate from the calculation of estimating the amount of eccentricity, so the amount of calculation is reduced. Therefore it is possible to quickly calculate the estimated amount.
In even yet another form of the invention, the calculation step comprises: a fifth calculation step of calculating the corrected state signal based on the error, the previously calculated state signal, estimated actuator gain and eccentricity estimation gain; a sixth calculation step of calculating the control signal from the corrected state signal; and a seventh calculation step of calculating the next state signal from the control signal and corrected state signal.
In this form of the invention, the eccentricity estimation observer is a current observer. Therefore it is suitable for processor processes.
Furthermore, in yet another form of the invention, the aforementioned fifth calculation step comprises: an eighth calculation step of calculating the corrected estimated position signal and estimated velocity schedule from the error, and estimated position signal and estimated velocity signal from the previous sample, and the estimated actuator gain; and a ninth calculation step of calculating the estimated eccentricity signal for the next sample from the aforementioned error, and the estimated eccentricity signal from the previous sample and the estimated eccentricity gain.
In the current observer of this form of the invention, the calculation for estimating the actuator operation and the calculation for estimating the amount of eccentricity are separate, so the amount of calculations is reduced. Therefore, it is possible to calculate the estimations quickly.
In another form of the invention, the calculation step comprises: a tenth calculation step of calculating the corrected estimated position signal and estimated velocity signal from the error, the previous estimated position signal and estimated velocity signal and the estimated actuator gain; an eleventh calculation step of calculating the control signal based on the corrected estimated position signal and previous estimated eccentricity signal; and a twelfth calculation step of calculating the estimated position signal, estimated velocity signal and estimated eccentricity signal for the next time, based on the corrected estimated position signal, corrected estimated velocity signal and previous estimated eccentricity signal.
In this form of the invention, since the calculation of the estimated eccentricity signal for the next time is performed after the calculation of the control signal, the time from when the position signal is sample until the control signal is output is shortened. Therefore, it is possible to quickly output the control signal.
Furthermore, another form of the invention comprises: a saving step of saving the estimated eccentricity signal for the head before changing when there is an instruction to change the head; and a step of reading the estimated eccentricity signal for the changed head and executing the aforementioned calculation steps with the read estimated eccentricity signal as the initial value.
In this form of the invention, since the amount of eccentricity varies for each head, or in other words for each surface of the disk medium, it is necessary to change the state variable for the eccentricity for each head. When doing this, the state variable for eccentricity is saved for each head, and by changing the state variable when changing heads, it is possible to initialize the eccentricity estimation observer with a state variable that matches that head.
In another form of the invention, the saving step comprises a saving step of saving the conversion value after the estimated eccentricity signal has been converted to an estimated eccentricity signal for the reference sector, and the execution step comprises a step of correcting the saved estimated eccentricity signal to an estimated eccentricity signal of the current sector.
In this form of the invention, when saving the initial value of the eccentricity estimation observer for each head, only two state variables need to be saved. Therefore, it is possible to reduce the amount of memory required for saving the state variable for eccentricity.